(1) Field of the Invention
The present invention relates generally to extrusion of plastic materials and, more particularly, to an apparatus for continuous forming hot melt adhesive cartridges.
(2) Description of the Prior Art
Commercial hot melt adhesives are used extensively in a variety of manufacturing applications. These applications include the attachment of furniture trim, packaging labels and profile caps. Typically, these adhesives are provided in cartridge form comprising cylinders of hardened adhesive having a diameter of between about 10 and 20 mm. Depending on the chemical makeup of the adhesive, the cylinders are extruded in continuous fashion through a conventional extruder using a similar process to that of plastic extrusion. However, this has only been true for the smaller sizes. The smaller sizes do not usually require external support since most of the compositions cool and harden quickly. Larger diameter cartridges, greater than about 43 mm, have required the use of single cavity mold to form the desired shape and allow sufficient time for cooling. For example, adhesives such as low tack ethylene vinyl acetate (EVA) are first pelletized and then fed into an extruder.
However, some commercial hot melt thermoplastic adhesives, such as high tack ethylene vinyl acetate (EVA) or amorphous polyalphaolefins (APAO), can not be extruded conventionally. This is because these compositions are so xe2x80x9ctackyxe2x80x9d that the pellets lump together and the plastic can not be extruded. That is, pellets formed from these adhesives do not flow readily but rather form a conglomerate mass that plugs the extruder feed chute. These types of adhesives must be formed using a batch process that involves filling a series of cylindrical molds with molten adhesive. The molds are cooled and the adhesive is trimmed and removed from the mold.
Even with best automation equipment available, the maximum through put using this batch process is between about 70 and 100 pounds per hour. In addition, the batch process is labor intensive and generates a large amount of scrap adhesive that must be recycled. In addition, it would be desirable if the palletizing step could be eliminated.
Thus, there is a need for an apparatus for forming thermoplastic adhesive cartridges which operates continuously while, at the same time, does not require that the thermoplastic adhesive be pelletized before use.
The present invention is directed to an apparatus for continuously forming thermoplastic adhesive cartridges. A molten thermoplastic adhesive supply provides a supply of molten adhesive to a pump downstream from the molten thermoplastic adhesive supply. The pump then provides a molten thermoplastic adhesive melt stream which passes through a screen filter downstream from the pump to prevent the discharge of impurities in the molten thermoplastic adhesive melt stream from the pump. A temperature-controlled conduit downstream from the pump then lowers the temperature of the molten plastic melt stream to closely above its softening point.
A continuous molder is located downstream from the melt pump for receiving the molten plastic melt stream from the melt pump to form the thermoplastic adhesive cartridge continuously. The continuous molder includes a molten mold material supply and a die head for receiving the molten mold material and forming a continuous mold. A cooling zone upstream from the discharge of the melt pump and downstream from the die head cools the molten mold material below its softening point temperature to form the continuous mold prior to receiving the molten thermoplastic adhesive.
The cooling zone includes a vacuum chamber for receiving the molten mold material from the die head and expanding the outer wall of the continuous mold outwardly. A calibrator assembly surrounds the continuous mold for controlling the outward expansion of the outer wall of the continuous mold. Finally, a cooling fluid surrounds the molten mold material to cool and solidify the mold material. A second cooling zone downstream from the discharge of the melt pump then cools the molten plastic melt stream discharged into the continuous mold below its softening point temperature to form the thermoplastic adhesive inside the continuous mold.
In addition, in the preferred embodiment, a conveyor downstream from the cooling zones moves the continuous mold and adhesive downstream at a speed proportion to the rate of discharge of the molten plastic material into the continuous mold.
Finally, a cutter downstream from the conveyor removes the continuous mold from the thermoplastic adhesive and cuts the adhesive into predetermined lengths for subsequent use.
Accordingly, one aspect of the present invention is to provide an apparatus for forming a plastic body. The apparatus includes: a molten plastic supply; a pump downstream from the molten plastic supply for providing a molten plastic melt stream; and a temperature-controlled conduit downstream from the pump for lowering the temperature of the molten plastic melt stream to closely above its softening point.
Another aspect of the present invention is to provide a melt pump for an apparatus for forming a thermoplastic adhesive cartridge. The apparatus includes: a molten thermoplastic adhesive supply; a pump downstream from the molten thermoplastic adhesive supply for providing a molten thermoplastic adhesive melt stream; a screen filter downstream from the pump for preventing the discharge of impurities in the molten thermoplastic adhesive melt stream from the pump; and a temperature-controlled conduit downstream from the pump for lowering the temperature of the molten plastic melt stream to closely above its softening point.
Still another aspect of the present invention is to provide an apparatus for continuously forming thermoplastic adhesive cartridges. The apparatus includes: a molten thermoplastic adhesive supply; a pump downstream from the molten thermoplastic adhesive supply for providing a molten thermoplastic adhesive melt stream; a screen filter downstream from the pump for preventing the discharge of impurities in the molten thermoplastic adhesive melt stream from the pump; a temperature-controlled conduit downstream from the pump for lowering the temperature of the molten plastic melt stream to closely above its softening point; and a continuous molder downstream from the melt pump for receiving the molten plastic melt stream from the melt pump.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the drawings.